Speakerphones allow several users at one end of a telephone connection to participate in the telephone conversation. Even in the case of a telephone conversation between two users, a speakerphone provides the advantage of allowing the user to participate in the conversation without having to hold a handset or wear a headset. Such hands-free operation gives the user the freedom to move about the room or type at a computer terminal while participating in the conversation.
Speakerphones have, however, one severe drawback. By necessity, the microphone of the speakerphone is nearer to the speaker in the speakerphone than to the user. Hence, feedback can become a problem if the speakerphone is run in full-duplex mode. While full-duplex speakerphones are known in the art, such speakerphones are relatively expensive. Hence, to solve the feedback problem in inexpensive speakerphones, the speakerphone is run in a half-duplex mode in which an internal monitoring circuit switches the speakerphone between "send" and "receive" modes thereby preventing the acoustical output of the speaker from being picked up by the microphone and causing feedback.
The internal monitoring circuit operates by detecting the voltages from the audio downlink from the telephone line and the voltage at the microphone of the speakerphone. A pair of attenuators are used to alternatively isolate the speaker or the microphone from the phone line. The attenuators are controlled by comparing the voice level on the microphone with the voice level being received on the telephone line. When the voice level at the microphone exceeds that on the incoming line by a predetermined amount, the microphone is given control of the telephone line and the speaker input is attenuated. When the level at the microphone drops below a level determined by a threshold value and the signal level on the telephone line, the output of the microphone is attenuated and the attenuation of the speaker input is removed.
The effective threshold at which a person using the speakerphone can take over a conversation depends on the signal level on the telephone line. If the person on the other end of the conversation speaks loudly, the speakerphone user must raise his or her voice to actuate the microphone of the speakerphone to gain control of the conversation. This problem with speakerphones often forces the user to speak at a level that is unnatural for that person. In some cases, the speakerphone user may be perceived as speaking in a rude manner when the user is merely trying to overcome a loud-voiced speaker at the other end of the conversation.
Broadly, it is the object of the present invention to provide an improved speakerphone.
It is a further object of the present invention to provide a speakerphone in which the user can adjust the level at which the user's voice causes the microphone on the user's speakerphone to take control of the speakerphone.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.